source: ps/trunk/source/graphics/Terrain.cpp@ 25266

/* Copyright (C) 2021 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 * Describes ground via heightmap and array of CPatch.
 */

#include "precompiled.h"

#include "lib/res/graphics/ogl_tex.h"
#include "lib/sysdep/cpu.h"

#include "renderer/Renderer.h"

#include "TerrainProperties.h"
#include "TerrainTextureEntry.h"
#include "TerrainTextureManager.h"

#include <string.h>
#include "Terrain.h"
#include "Patch.h"
#include "maths/FixedVector3D.h"
#include "maths/MathUtil.h"
#include "ps/CLogger.h"
#include "simulation2/helpers/Pathfinding.h"

///////////////////////////////////////////////////////////////////////////////
// CTerrain constructor
CTerrain::CTerrain()
: m_Heightmap(0), m_Patches(0), m_MapSize(0), m_MapSizePatches(0),
m_BaseColor(255, 255, 255, 255)
{
}

///////////////////////////////////////////////////////////////////////////////
// CTerrain constructor
CTerrain::~CTerrain()
{
    ReleaseData();
}


///////////////////////////////////////////////////////////////////////////////
// ReleaseData: delete any data allocated by this terrain
void CTerrain::ReleaseData()
{
    m_HeightMipmap.ReleaseData();

    delete[] m_Heightmap;
    delete[] m_Patches;
}


///////////////////////////////////////////////////////////////////////////////
// Initialise: initialise this terrain to the given size
// using given heightmap to setup elevation data
bool CTerrain::Initialize(ssize_t patchesPerSide, const u16* data)
{
    // clean up any previous terrain
    ReleaseData();

    // store terrain size
    m_MapSize = patchesPerSide * PATCH_SIZE + 1;
    m_MapSizePatches = patchesPerSide;
    // allocate data for new terrain
    m_Heightmap = new u16[m_MapSize * m_MapSize];
    m_Patches = new CPatch[m_MapSizePatches * m_MapSizePatches];

    // given a heightmap?
    if (data)
    {
        // yes; keep a copy of it
        memcpy(m_Heightmap, data, m_MapSize*m_MapSize*sizeof(u16));
    }
    else
    {
        // build a flat terrain
        memset(m_Heightmap, 0, m_MapSize*m_MapSize*sizeof(u16));
    }

    // setup patch parents, indices etc
    InitialisePatches();

    // initialise mipmap
    m_HeightMipmap.Initialize(m_MapSize, m_Heightmap);

    return true;
}

///////////////////////////////////////////////////////////////////////////////

CStr8 CTerrain::GetMovementClass(ssize_t i, ssize_t j) const
{
    CMiniPatch* tile = GetTile(i, j);
    if (tile && tile->GetTextureEntry())
        return tile->GetTextureEntry()->GetProperties().GetMovementClass();

    return "default";
}

///////////////////////////////////////////////////////////////////////////////
// CalcPosition: calculate the world space position of the vertex at (i,j)
// If i,j is off the map, it acts as if the edges of the terrain are extended
// outwards to infinity
void CTerrain::CalcPosition(ssize_t i, ssize_t j, CVector3D& pos) const
{
    ssize_t hi = Clamp(i, 0, m_MapSize - 1);
    ssize_t hj = Clamp(j, 0, m_MapSize - 1);
    u16 height = m_Heightmap[hj*m_MapSize + hi];
    pos.X = float(i*TERRAIN_TILE_SIZE);
    pos.Y = float(height*HEIGHT_SCALE);
    pos.Z = float(j*TERRAIN_TILE_SIZE);
}

///////////////////////////////////////////////////////////////////////////////
// CalcPositionFixed: calculate the world space position of the vertex at (i,j)
void CTerrain::CalcPositionFixed(ssize_t i, ssize_t j, CFixedVector3D& pos) const
{
    ssize_t hi = Clamp(i, 0, m_MapSize - 1);
    ssize_t hj = Clamp(j, 0, m_MapSize - 1);
    u16 height = m_Heightmap[hj*m_MapSize + hi];
    pos.X = fixed::FromInt(i) * (int)TERRAIN_TILE_SIZE;
    // fixed max value is 32767, but height is a u16, so divide by two to avoid overflow
    pos.Y = fixed::FromInt(height/ 2 ) / ((int)HEIGHT_UNITS_PER_METRE / 2);
    pos.Z = fixed::FromInt(j) * (int)TERRAIN_TILE_SIZE;
}


///////////////////////////////////////////////////////////////////////////////
// CalcNormal: calculate the world space normal of the vertex at (i,j)
void CTerrain::CalcNormal(ssize_t i, ssize_t j, CVector3D& normal) const
{
    CVector3D left, right, up, down;

    // Calculate normals of the four half-tile triangles surrounding this vertex:

    // get position of vertex where normal is being evaluated
    CVector3D basepos;
    CalcPosition(i, j, basepos);

    if (i > 0) {
        CalcPosition(i-1, j, left);
        left -= basepos;
        left.Normalize();
    }

    if (i < m_MapSize-1) {
        CalcPosition(i+1, j, right);
        right -= basepos;
        right.Normalize();
    }

    if (j > 0) {
        CalcPosition(i, j-1, up);
        up -= basepos;
        up.Normalize();
    }

    if (j < m_MapSize-1) {
        CalcPosition(i, j+1, down);
        down -= basepos;
        down.Normalize();
    }

    CVector3D n0 = up.Cross(left);
    CVector3D n1 = left.Cross(down);
    CVector3D n2 = down.Cross(right);
    CVector3D n3 = right.Cross(up);

    // Compute the mean of the normals
    normal = n0 + n1 + n2 + n3;
    float nlen=normal.Length();
    if (nlen>0.00001f) normal*=1.0f/nlen;
}

///////////////////////////////////////////////////////////////////////////////
// CalcNormalFixed: calculate the world space normal of the vertex at (i,j)
void CTerrain::CalcNormalFixed(ssize_t i, ssize_t j, CFixedVector3D& normal) const
{
    CFixedVector3D left, right, up, down;

    // Calculate normals of the four half-tile triangles surrounding this vertex:

    // get position of vertex where normal is being evaluated
    CFixedVector3D basepos;
    CalcPositionFixed(i, j, basepos);

    if (i > 0) {
        CalcPositionFixed(i-1, j, left);
        left -= basepos;
        left.Normalize();
    }

    if (i < m_MapSize-1) {
        CalcPositionFixed(i+1, j, right);
        right -= basepos;
        right.Normalize();
    }

    if (j > 0) {
        CalcPositionFixed(i, j-1, up);
        up -= basepos;
        up.Normalize();
    }

    if (j < m_MapSize-1) {
        CalcPositionFixed(i, j+1, down);
        down -= basepos;
        down.Normalize();
    }

    CFixedVector3D n0 = up.Cross(left);
    CFixedVector3D n1 = left.Cross(down);
    CFixedVector3D n2 = down.Cross(right);
    CFixedVector3D n3 = right.Cross(up);

    // Compute the mean of the normals
    normal = n0 + n1 + n2 + n3;
    normal.Normalize();
}

CVector3D CTerrain::CalcExactNormal(float x, float z) const
{
    // Clamp to size-2 so we can use the tiles (xi,zi)-(xi+1,zi+1)
    const ssize_t xi = Clamp<ssize_t>(floor(x / TERRAIN_TILE_SIZE), 0, m_MapSize - 2);
    const ssize_t zi = Clamp<ssize_t>(floor(z / TERRAIN_TILE_SIZE), 0, m_MapSize - 2);

    const float xf = Clamp(x / TERRAIN_TILE_SIZE-xi, 0.0f, 1.0f);
    const float zf = Clamp(z / TERRAIN_TILE_SIZE-zi, 0.0f, 1.0f);

    float h00 = m_Heightmap[zi*m_MapSize + xi];
    float h01 = m_Heightmap[(zi+1)*m_MapSize + xi];
    float h10 = m_Heightmap[zi*m_MapSize + (xi+1)];
    float h11 = m_Heightmap[(zi+1)*m_MapSize + (xi+1)];

    // Determine which terrain triangle this point is on,
    // then compute the normal of that triangle's plane

    if (GetTriangulationDir(xi, zi))
    {
        if (xf + zf <= 1.f)
        {
            // Lower-left triangle (don't use h11)
            return -CVector3D(TERRAIN_TILE_SIZE, (h10-h00)*HEIGHT_SCALE, 0).Cross(CVector3D(0, (h01-h00)*HEIGHT_SCALE, TERRAIN_TILE_SIZE)).Normalized();
        }
        else
        {
            // Upper-right triangle (don't use h00)
            return -CVector3D(TERRAIN_TILE_SIZE, (h11-h01)*HEIGHT_SCALE, 0).Cross(CVector3D(0, (h11-h10)*HEIGHT_SCALE, TERRAIN_TILE_SIZE)).Normalized();
        }
    }
    else
    {
        if (xf <= zf)
        {
            // Upper-left triangle (don't use h10)
            return -CVector3D(TERRAIN_TILE_SIZE, (h11-h01)*HEIGHT_SCALE, 0).Cross(CVector3D(0, (h01-h00)*HEIGHT_SCALE, TERRAIN_TILE_SIZE)).Normalized();
        }
        else
        {
            // Lower-right triangle (don't use h01)
            return -CVector3D(TERRAIN_TILE_SIZE, (h10-h00)*HEIGHT_SCALE, 0).Cross(CVector3D(0, (h11-h10)*HEIGHT_SCALE, TERRAIN_TILE_SIZE)).Normalized();
        }
    }
}

///////////////////////////////////////////////////////////////////////////////
// GetPatch: return the patch at (i,j) in patch space, or null if the patch is
// out of bounds
CPatch* CTerrain::GetPatch(ssize_t i, ssize_t j) const
{
    // range check (invalid indices are passed in by the culling and
    // patch blend code because they iterate from 0..#patches and examine
    // neighbors without checking if they're already on the edge)
    if( (size_t)i >= (size_t)m_MapSizePatches || (size_t)j >= (size_t)m_MapSizePatches )
        return 0;

    return &m_Patches[(j*m_MapSizePatches)+i];
}


///////////////////////////////////////////////////////////////////////////////
// GetTile: return the tile at (i,j) in tile space, or null if the tile is out
// of bounds
CMiniPatch* CTerrain::GetTile(ssize_t i, ssize_t j) const
{
    // see comment above
    if( (size_t)i >= (size_t)(m_MapSize-1) || (size_t)j >= (size_t)(m_MapSize-1) )
        return 0;

    CPatch* patch=GetPatch(i/PATCH_SIZE, j/PATCH_SIZE); // can't fail (due to above check)
    return &patch->m_MiniPatches[j%PATCH_SIZE][i%PATCH_SIZE];
}

float CTerrain::GetVertexGroundLevel(ssize_t i, ssize_t j) const
{
    i = Clamp(i, 0, m_MapSize - 1);
    j = Clamp(j, 0, m_MapSize - 1);
    return HEIGHT_SCALE * m_Heightmap[j*m_MapSize + i];
}

fixed CTerrain::GetVertexGroundLevelFixed(ssize_t i, ssize_t j) const
{
    i = Clamp(i, 0, m_MapSize - 1);
    j = Clamp(j, 0, m_MapSize - 1);
    // Convert to fixed metres (being careful to avoid intermediate overflows)
    return fixed::FromInt(m_Heightmap[j*m_MapSize + i] / 2) / (int)(HEIGHT_UNITS_PER_METRE / 2);
}

fixed CTerrain::GetSlopeFixed(ssize_t i, ssize_t j) const
{
    // Clamp to size-2 so we can use the tiles (i,j)-(i+1,j+1)
    i = Clamp(i, 0, m_MapSize - 2);
    j = Clamp(j, 0, m_MapSize - 2);

    u16 h00 = m_Heightmap[j*m_MapSize + i];
    u16 h01 = m_Heightmap[(j+1)*m_MapSize + i];
    u16 h10 = m_Heightmap[j*m_MapSize + (i+1)];
    u16 h11 = m_Heightmap[(j+1)*m_MapSize + (i+1)];

    // Difference of highest point from lowest point
    u16 delta = std::max(std::max(h00, h01), std::max(h10, h11)) -
                std::min(std::min(h00, h01), std::min(h10, h11));

    // Compute fractional slope (being careful to avoid intermediate overflows)
    return fixed::FromInt(delta / TERRAIN_TILE_SIZE) / (int)HEIGHT_UNITS_PER_METRE;
}

fixed CTerrain::GetExactSlopeFixed(fixed x, fixed z) const
{
    // Clamp to size-2 so we can use the tiles (xi,zi)-(xi+1,zi+1)
    const ssize_t xi = Clamp<ssize_t>((x / static_cast<int>(TERRAIN_TILE_SIZE)).ToInt_RoundToZero(), 0, m_MapSize - 2);
    const ssize_t zi = Clamp<ssize_t>((z / static_cast<int>(TERRAIN_TILE_SIZE)).ToInt_RoundToZero(), 0, m_MapSize - 2);

    const fixed one = fixed::FromInt(1);

    const fixed xf = Clamp((x / static_cast<int>(TERRAIN_TILE_SIZE)) - fixed::FromInt(xi), fixed::Zero(), one);
    const fixed zf = Clamp((z / static_cast<int>(TERRAIN_TILE_SIZE)) - fixed::FromInt(zi), fixed::Zero(), one);

    u16 h00 = m_Heightmap[zi*m_MapSize + xi];
    u16 h01 = m_Heightmap[(zi+1)*m_MapSize + xi];
    u16 h10 = m_Heightmap[zi*m_MapSize + (xi+1)];
    u16 h11 = m_Heightmap[(zi+1)*m_MapSize + (xi+1)];

    u16 delta;
    if (GetTriangulationDir(xi, zi))
    {
        if (xf + zf <= one)
        {
            // Lower-left triangle (don't use h11)
            delta = std::max(std::max(h00, h01), h10) -
                    std::min(std::min(h00, h01), h10);
        }
        else
        {
            // Upper-right triangle (don't use h00)
            delta = std::max(std::max(h01, h10), h11) -
                    std::min(std::min(h01, h10), h11);
        }
    }
    else
    {
        if (xf <= zf)
        {
            // Upper-left triangle (don't use h10)
            delta = std::max(std::max(h00, h01), h11) -
                    std::min(std::min(h00, h01), h11);
        }
        else
        {
            // Lower-right triangle (don't use h01)
            delta = std::max(std::max(h00, h10), h11) -
                    std::min(std::min(h00, h10), h11);
        }
    }

    // Compute fractional slope (being careful to avoid intermediate overflows)
    return fixed::FromInt(delta / TERRAIN_TILE_SIZE) / (int)HEIGHT_UNITS_PER_METRE;
}

float CTerrain::GetFilteredGroundLevel(float x, float z, float radius) const
{
    // convert to [0,1] interval
    float nx = x / (TERRAIN_TILE_SIZE*m_MapSize);
    float nz = z / (TERRAIN_TILE_SIZE*m_MapSize);
    float nr = radius / (TERRAIN_TILE_SIZE*m_MapSize);

    // get trilinear filtered mipmap height
    return HEIGHT_SCALE * m_HeightMipmap.GetTrilinearGroundLevel(nx, nz, nr);
}

float CTerrain::GetExactGroundLevel(float x, float z) const
{
    // Clamp to size-2 so we can use the tiles (xi,zi)-(xi+1,zi+1)
    const ssize_t xi = Clamp<ssize_t>(floor(x / TERRAIN_TILE_SIZE), 0, m_MapSize - 2);
    const ssize_t zi = Clamp<ssize_t>(floor(z / TERRAIN_TILE_SIZE), 0, m_MapSize - 2);

    const float xf = Clamp(x / TERRAIN_TILE_SIZE - xi, 0.0f, 1.0f);
    const float zf = Clamp(z / TERRAIN_TILE_SIZE - zi, 0.0f, 1.0f);

    float h00 = m_Heightmap[zi*m_MapSize + xi];
    float h01 = m_Heightmap[(zi+1)*m_MapSize + xi];
    float h10 = m_Heightmap[zi*m_MapSize + (xi+1)];
    float h11 = m_Heightmap[(zi+1)*m_MapSize + (xi+1)];

    // Determine which terrain triangle this point is on,
    // then compute the linearly-interpolated height on that triangle's plane

    if (GetTriangulationDir(xi, zi))
    {
        if (xf + zf <= 1.f)
        {
            // Lower-left triangle (don't use h11)
            return HEIGHT_SCALE * (h00 + (h10-h00)*xf + (h01-h00)*zf);
        }
        else
        {
            // Upper-right triangle (don't use h00)
            return HEIGHT_SCALE * (h11 + (h01-h11)*(1-xf) + (h10-h11)*(1-zf));
        }
    }
    else
    {
        if (xf <= zf)
        {
            // Upper-left triangle (don't use h10)
            return HEIGHT_SCALE * (h00 + (h11-h01)*xf + (h01-h00)*zf);
        }
        else
        {
            // Lower-right triangle (don't use h01)
            return HEIGHT_SCALE * (h00 + (h10-h00)*xf + (h11-h10)*zf);
        }
    }
}

fixed CTerrain::GetExactGroundLevelFixed(fixed x, fixed z) const
{
    // Clamp to size-2 so we can use the tiles (xi,zi)-(xi+1,zi+1)
    const ssize_t xi = Clamp<ssize_t>((x / static_cast<int>(TERRAIN_TILE_SIZE)).ToInt_RoundToZero(), 0, m_MapSize - 2);
    const ssize_t zi = Clamp<ssize_t>((z / static_cast<int>(TERRAIN_TILE_SIZE)).ToInt_RoundToZero(), 0, m_MapSize - 2);

    const fixed one = fixed::FromInt(1);

    const fixed xf = Clamp((x / static_cast<int>(TERRAIN_TILE_SIZE)) - fixed::FromInt(xi), fixed::Zero(), one);
    const fixed zf = Clamp((z / static_cast<int>(TERRAIN_TILE_SIZE)) - fixed::FromInt(zi), fixed::Zero(), one);

    u16 h00 = m_Heightmap[zi*m_MapSize + xi];
    u16 h01 = m_Heightmap[(zi+1)*m_MapSize + xi];
    u16 h10 = m_Heightmap[zi*m_MapSize + (xi+1)];
    u16 h11 = m_Heightmap[(zi+1)*m_MapSize + (xi+1)];

    // Intermediate scaling of xf, so we don't overflow in the multiplications below
    // (h00 <= 65535, xf <= 1, max fixed is < 32768; divide by 2 here so xf1*h00 <= 32767.5)
    const fixed xf0 = xf / 2;
    const fixed xf1 = (one - xf) / 2;

    // Linearly interpolate
    return ((one - zf).Multiply(xf1 * h00 + xf0 * h10)
                  + zf.Multiply(xf1 * h01 + xf0 * h11)) / (int)(HEIGHT_UNITS_PER_METRE / 2);

    // TODO: This should probably be more like GetExactGroundLevel()
    // in handling triangulation properly
}

bool CTerrain::GetTriangulationDir(ssize_t i, ssize_t j) const
{
    // Clamp to size-2 so we can use the tiles (i,j)-(i+1,j+1)
    i = Clamp(i, 0, m_MapSize - 2);
    j = Clamp(j, 0, m_MapSize - 2);

    int h00 = m_Heightmap[j*m_MapSize + i];
    int h01 = m_Heightmap[(j+1)*m_MapSize + i];
    int h10 = m_Heightmap[j*m_MapSize + (i+1)];
    int h11 = m_Heightmap[(j+1)*m_MapSize + (i+1)];

    // Prefer triangulating in whichever direction means the midpoint of the diagonal
    // will be the highest. (In particular this means a diagonal edge will be straight
    // along the top, and jagged along the bottom, which makes sense for terrain.)
    int mid1 = h00+h11;
    int mid2 = h01+h10;
    return (mid1 < mid2);
}

void CTerrain::ResizeAndOffset(ssize_t size, ssize_t horizontalOffset, ssize_t verticalOffset)
{
    if (size == m_MapSizePatches && horizontalOffset == 0 && verticalOffset == 0)
    {
        // Inexplicable request to resize terrain to the same size, ignore it.
        return;
    }

    if (!m_Heightmap ||
        std::abs(horizontalOffset) >= size / 2 + m_MapSizePatches / 2 ||
        std::abs(verticalOffset) >= size / 2 + m_MapSizePatches / 2)
    {
        // We have not yet created a terrain, or we are offsetting outside the current source.
        // Let's build a default terrain of the given size now.
        Initialize(size, 0);
        return;
    }

    // Allocate data for new terrain.
    const ssize_t newMapSize = size * PATCH_SIZE + 1;
    u16* newHeightmap = new u16[newMapSize * newMapSize];
    memset(newHeightmap, 0, newMapSize * newMapSize * sizeof(u16));
    CPatch* newPatches = new CPatch[size * size];

    // O--------------------+
    // | Source             |
    // |                    |
    // | Source Center (SC) |
    // |          X         |
    // |             A------+----------------+
    // |             |      |    Destination |
    // |             |      |                |
    // +-------------+------B                |
    //               |    Dest. Center (DC)  |
    //               |           X           |
    //               |                       |
    //               |                       |
    //               |                       |
    //               |                       |
    //               +-----------------------+
    //
    // Calculations below should also account cases like:
    //
    // +----------+   +----------+     +----------+   +---+--+---+   +------+
    // |S         |   |D         |     |S         |   |S  |  |  D|   |D     |
    // |   +---+  |   |   +---+  |   +-+-+        |   |   |  |   |   |  +---+--+
    // |   | D |  |   |   | S |  |   |D| |        |   +---+--+---+   +--+---+  |
    // |   +---+  |   |   +---+  |   +-+-+        |                     |     S|
    // +----------+   +----------+     +----------+                     +------+
    //
    // O = (0, 0)
    // SC = (m_MapSizePatches / 2, m_MapSizePatches / 2)
    // DC - SC = (horizontalOffset, verticalOffset)
    //
    // Source upper left:
    // A = (max(0, (m_MapSizePatches - size) / 2 + horizontalOffset),
    //      max(0, (m_MapSizePatches - size) / 2 + verticalOffset))
    // Source bottom right:
    // B = (min(m_MapSizePatches, (m_MapSizePatches + size) / 2 + horizontalOffset),
    //      min(m_MapSizePatches, (m_MapSizePatches + size) / 2 + verticalOffset))
    //
    // A-B is the area that we have to copy from the source to the destination.

    // Restate center offset as a window over destination.
    // This has the effect of always considering the source to be the same size or smaller.
    const ssize_t sourceUpperLeftX = std::max(
        static_cast<ssize_t>(0), m_MapSizePatches / 2 - size / 2 + horizontalOffset);
    const ssize_t sourceUpperLeftZ = std::max(
        static_cast<ssize_t>(0), m_MapSizePatches / 2 - size / 2 + verticalOffset);

    const ssize_t destUpperLeftX = std::max(
        static_cast<ssize_t>(0), (size / 2 - m_MapSizePatches / 2 - horizontalOffset));
    const ssize_t destUpperLeftZ = std::max(
        static_cast<ssize_t>(0), (size / 2 - m_MapSizePatches / 2 - verticalOffset));

    const ssize_t width =
        std::min(m_MapSizePatches, m_MapSizePatches / 2 + horizontalOffset + size / 2) - sourceUpperLeftX;
    const ssize_t depth =
        std::min(m_MapSizePatches, m_MapSizePatches / 2 + verticalOffset + size / 2) - sourceUpperLeftZ;

    for (ssize_t j = 0; j < depth * PATCH_SIZE; ++j)
    {
        // Copy the main part from the source. Destination heightmap:
        // +----------+
        // |          |
        // |   1234   | < current j-th row for example.
        // |   5678   |
        // |          |
        // +----------+
        u16* dst = newHeightmap + (j + destUpperLeftZ * PATCH_SIZE) * newMapSize + destUpperLeftX * PATCH_SIZE;
        u16* src = m_Heightmap + (j + sourceUpperLeftZ * PATCH_SIZE) * m_MapSize + sourceUpperLeftX * PATCH_SIZE;
        std::copy_n(src, width * PATCH_SIZE, dst);
        if (destUpperLeftX > 0)
        {
            // Fill the preceding part by copying the first elements of the
            // main part. Destination heightmap:
            // +----------+
            // |          |
            // |1111234   |  < current j-th row for example.
            // |   5678   |
            // |          |
            // +----------+
            u16* dst_prefix = newHeightmap + (j + destUpperLeftZ * PATCH_SIZE) * newMapSize;
            std::fill_n(dst_prefix, destUpperLeftX * PATCH_SIZE, dst[0]);
        }
        if ((destUpperLeftX + width) * PATCH_SIZE < newMapSize)
        {
            // Fill the succeeding part by copying the last elements of the
            // main part. Destination heightmap:
            // +----------+
            // |          |
            // |1111234444|  < current j-th row for example.
            // |   5678   |
            // |          |
            // +----------+
            u16* dst_suffix = dst + width * PATCH_SIZE;
            std::fill_n(
                dst_suffix,
                newMapSize - (width + destUpperLeftX) * PATCH_SIZE,
                dst[width * PATCH_SIZE - 1]);
        }
    }
    // Copy over heights from the preceding row. Destination heightmap:
    // +----------+
    // |1111234444| < copied from the row below
    // |1111234444|
    // |5555678888|
    // |          |
    // +----------+
    for (ssize_t j = 0; j < destUpperLeftZ * PATCH_SIZE; ++j)
    {

        u16* dst = newHeightmap + j * newMapSize;
        u16* src = newHeightmap + destUpperLeftZ * PATCH_SIZE * newMapSize;
        std::copy_n(src, newMapSize, dst);
    }
    // Copy over heights from the succeeding row. Destination heightmap:
    // +----------+
    // |1111234444|
    // |1111234444|
    // |5555678888|
    // |5555678888| < copied from the row above
    // +----------+
    for (ssize_t j = (destUpperLeftZ + depth) * PATCH_SIZE; j < newMapSize; ++j)
    {
        u16* dst = newHeightmap + j * newMapSize;
        u16* src = newHeightmap + ((destUpperLeftZ + depth) * PATCH_SIZE - 1) * newMapSize;
        std::copy_n(src, newMapSize, dst);
    }

    // Now build new patches. The same process as for the heightmap.
    for (ssize_t j = 0; j < depth; ++j)
    {
        for (ssize_t i = 0; i < width; ++i)
        {
            const CPatch& src =
                m_Patches[(sourceUpperLeftZ + j) * m_MapSizePatches + sourceUpperLeftX + i];
            CPatch& dst =
                newPatches[(destUpperLeftZ + j) * size + destUpperLeftX + i];
            std::copy_n(&src.m_MiniPatches[0][0], PATCH_SIZE * PATCH_SIZE, &dst.m_MiniPatches[0][0]);
        }
        for (ssize_t i = 0; i < destUpperLeftX; ++i)
            for (ssize_t jPatch = 0; jPatch < PATCH_SIZE; ++jPatch)
            {
                const CMiniPatch& src =
                    newPatches[(destUpperLeftZ + j) * size + destUpperLeftX]
                        .m_MiniPatches[jPatch][0];
                for (ssize_t iPatch = 0; iPatch < PATCH_SIZE; ++iPatch)
                {
                    CMiniPatch& dst =
                        newPatches[(destUpperLeftZ + j) * size + i]
                            .m_MiniPatches[jPatch][iPatch];
                    dst = src;
                }
            }
        for (ssize_t i = destUpperLeftX + width; i < size; ++i)
        {
            for (ssize_t jPatch = 0; jPatch < PATCH_SIZE; ++jPatch)
            {
                const CMiniPatch& src =
                    newPatches[(destUpperLeftZ + j) * size + destUpperLeftX + width - 1]
                        .m_MiniPatches[jPatch][PATCH_SIZE - 1];
                for (ssize_t iPatch = 0; iPatch < PATCH_SIZE; ++iPatch)
                {
                    CMiniPatch& dst =
                        newPatches[(destUpperLeftZ + j) * size + i].m_MiniPatches[jPatch][iPatch];
                    dst = src;
                }
            }
        }
    }

    for (ssize_t j = 0; j < destUpperLeftZ; ++j)
        for (ssize_t i = 0; i < size; ++i)
            for (ssize_t iPatch = 0; iPatch < PATCH_SIZE; ++iPatch)
            {
                const CMiniPatch& src =
                    newPatches[destUpperLeftZ * size + i].m_MiniPatches[0][iPatch];
                for (ssize_t jPatch = 0; jPatch < PATCH_SIZE; ++jPatch)
                {
                    CMiniPatch& dst =
                        newPatches[j * size + i].m_MiniPatches[jPatch][iPatch];
                    dst = src;
                }
            }
    for (ssize_t j = destUpperLeftZ + depth; j < size; ++j)
        for (ssize_t i = 0; i < size; ++i)
            for (ssize_t iPatch = 0; iPatch < PATCH_SIZE; ++iPatch)
            {
                const CMiniPatch& src =
                    newPatches[(destUpperLeftZ + depth - 1) * size + i].m_MiniPatches[0][iPatch];
                for (ssize_t jPatch = 0; jPatch < PATCH_SIZE; ++jPatch)
                {
                    CMiniPatch& dst =
                        newPatches[j * size + i].m_MiniPatches[jPatch][iPatch];
                    dst = src;
                }
            }

    // Release all the original data.
    ReleaseData();

    // Store new data.
    m_Heightmap = newHeightmap;
    m_Patches = newPatches;
    m_MapSize = newMapSize;
    m_MapSizePatches = size;

    // Initialise all the new patches.
    InitialisePatches();

    // Initialise mipmap.
    m_HeightMipmap.Initialize(m_MapSize, m_Heightmap);
}

///////////////////////////////////////////////////////////////////////////////
// InitialisePatches: initialise patch data
void CTerrain::InitialisePatches()
{
    for (ssize_t j = 0; j < m_MapSizePatches; j++)
    {
        for (ssize_t i = 0; i < m_MapSizePatches; i++)
        {
            CPatch* patch = GetPatch(i, j); // can't fail
            patch->Initialize(this, i, j);
        }
    }
}

///////////////////////////////////////////////////////////////////////////////
// SetHeightMap: set up a new heightmap from 16-bit source data;
// assumes heightmap matches current terrain size
void CTerrain::SetHeightMap(u16* heightmap)
{
    // keep a copy of the given heightmap
    memcpy(m_Heightmap, heightmap, m_MapSize*m_MapSize*sizeof(u16));

    // recalculate patch bounds, invalidate vertices
    for (ssize_t j = 0; j < m_MapSizePatches; j++)
    {
        for (ssize_t i = 0; i < m_MapSizePatches; i++)
        {
            CPatch* patch = GetPatch(i, j); // can't fail
            patch->InvalidateBounds();
            patch->SetDirty(RENDERDATA_UPDATE_VERTICES);
        }
    }

    // update mipmap
    m_HeightMipmap.Update(m_Heightmap);
}


///////////////////////////////////////////////////////////////////////////////

void CTerrain::MakeDirty(ssize_t i0, ssize_t j0, ssize_t i1, ssize_t j1, int dirtyFlags)
{
    // Finds the inclusive limits of the patches that include the specified range of tiles
    ssize_t pi0 = Clamp( i0   /PATCH_SIZE, 0, m_MapSizePatches-1);
    ssize_t pi1 = Clamp((i1-1)/PATCH_SIZE, 0, m_MapSizePatches-1);
    ssize_t pj0 = Clamp( j0   /PATCH_SIZE, 0, m_MapSizePatches-1);
    ssize_t pj1 = Clamp((j1-1)/PATCH_SIZE, 0, m_MapSizePatches-1);

    for (ssize_t j = pj0; j <= pj1; j++)
    {
        for (ssize_t i = pi0; i <= pi1; i++)
        {
            CPatch* patch = GetPatch(i, j); // can't fail (i,j were clamped)
            if (dirtyFlags & RENDERDATA_UPDATE_VERTICES)
                patch->CalcBounds();
            patch->SetDirty(dirtyFlags);
        }
    }

    if (m_Heightmap)
    {
        m_HeightMipmap.Update(m_Heightmap,
            Clamp(i0, 0, m_MapSize - 1),
            Clamp(j0, 0, m_MapSize - 1),
            Clamp(i1, 1, m_MapSize),
            Clamp(j1, 1, m_MapSize)
        );
    }
}

void CTerrain::MakeDirty(int dirtyFlags)
{
    for (ssize_t j = 0; j < m_MapSizePatches; j++)
    {
        for (ssize_t i = 0; i < m_MapSizePatches; i++)
        {
            CPatch* patch = GetPatch(i, j); // can't fail
            if (dirtyFlags & RENDERDATA_UPDATE_VERTICES)
                patch->CalcBounds();
            patch->SetDirty(dirtyFlags);
        }
    }

    if (m_Heightmap)
        m_HeightMipmap.Update(m_Heightmap);
}

CBoundingBoxAligned CTerrain::GetVertexesBound(ssize_t i0, ssize_t j0, ssize_t i1, ssize_t j1)
{
    i0 = Clamp(i0, 0, m_MapSize - 1);
    j0 = Clamp(j0, 0, m_MapSize - 1);
    i1 = Clamp(i1, 0, m_MapSize - 1);
    j1 = Clamp(j1, 0, m_MapSize - 1);

    u16 minH = 65535;
    u16 maxH = 0;

    for (ssize_t j = j0; j <= j1; ++j)
    {
        for (ssize_t i = i0; i <= i1; ++i)
        {
            minH = std::min(minH, m_Heightmap[j*m_MapSize + i]);
            maxH = std::max(maxH, m_Heightmap[j*m_MapSize + i]);
        }
    }

    CBoundingBoxAligned bound;
    bound[0].X = (float)(i0*TERRAIN_TILE_SIZE);
    bound[0].Y = (float)(minH*HEIGHT_SCALE);
    bound[0].Z = (float)(j0*TERRAIN_TILE_SIZE);
    bound[1].X = (float)(i1*TERRAIN_TILE_SIZE);
    bound[1].Y = (float)(maxH*HEIGHT_SCALE);
    bound[1].Z = (float)(j1*TERRAIN_TILE_SIZE);
    return bound;
}